Generally, for autonomous running of a mobile object such as a mobile robot and an intelligent vehicle, it is necessary to detect in real time which point of a map the mobile object currently exists and which orientation the mobile object heads for. Particularly, since a same control command completely changes a next proceeding orientation depending on the orientation of the robot and vehicle, orientation information is a very important factor in movement control of the mobile object.
A variety of methods using radio wave, ultrasonic wave, RFID (Radio Frequency IDentification), image recognition and odometry are used for a position detection unit for detecting the position of the mobile object. Although some of position detection units provide orientation information with position information, most of them provide only position information.
For example, a global positioning system (GPS) can provide an absolute position within a very wide range, but cannot provide orientation information of the mobile object. A remote camera can relatively easily sense the mobile object and check its position via image recognition, but needs advanced image processing to check the orientation of the mobile object or needs to attach an orientation indicator to the mobile object.
In addition, when the position detection unit which cannot provide the orientation information is employed, a method for calculating a movement orientation vector from mobile object's position differences of a mobile object with a lapse of time, and determining the movement orientation as a current heading of the mobile object has been generally used to determine the orientation of the mobile object. However, this method has a disadvantage in that accurate orientation information is not provided, when the mobile object rotates in one place or moves in a curved route.
Moreover, an odometry method using an odometer is also used for detecting a position of a mobile object. This method measures a rotation number of a wheel by using an encoder sensor attached onto the wheel, and detects a relative position change of the mobile object by using an interval between the wheels and a diameter of the wheel. The method using the odometry provides a very high sampling rate and a relatively high precision in a short distance. Since, however, it reflects only a relative position change from a previous position, an error is accumulated due to sliding of the wheels or the like with increase of a running distance.
That is, as described above, the conventional position detection methods using the ultrasonic wave, radio wave, remote camera, or the like are not capable of providing the orientation information and high sampling rate, so that they are not preferably applied to the position detection unit for the autonomous running of the mobile object.